1. Field of the Invention
In one aspect this invention relates to diesel engine controls. In a further aspect this invention relates to diesel engine starting systems.
2. Prior Art
In general, diesel engines require the use of a starting aid particularly when engine starting is attempted in cold weather. The starting aid is used until there is sufficient heat in the cylinder area to sustain knock ignition combustion. At present two different methods are normally used to aid diesel engine starting. One method is ether injection, which provides a source of ether to the combustion chamber, the ether is highly combustible and causes fuel ignition even at low temperatures. This however requires that the ether supply be replenished and adds another fluid to be maintained. Such systems are also very expensive to install making them unsuitable for smaller engines where cost is a important factor.
A second method is to provide a glow plug or similar device which is heated to a temperature that will ignite at least a portion of any fuel injected into the combustion cylinder. The glow plugs continue to assist in igniting fuel until the combustion cylinder has reached a satisfactory operating temperature for knock ignition. The glow plugs can be heated after the engine has started operation to assist fuel combustion thereby minimizing the production of incomplete combustion products. Glow plug starting systems generally have one or more glow plugs associated with each combustion cylinder, a controller circuit to provide electrical current to the glow plug and a power source.
In greater detail, the most traditional prior art system for diesel engine control would include: a glow plug controller which acts through another control box containing a relay connection, the relay in turn activates the glow plugs, starter and related accessories. In such a system upon cold starting, the relay will engage and the glow plugs are activated for a set period of time to attain an operating temperature and then the starter is engaged. The engine is cranked L11 until it starts and assumes normal operation, or the starter is deactivated. During the start cycle, the relay is periodically energized to keep the glow plug temperature near the desired operating temperature of 1800 to 1900 F (about 1000 to 1050 C). The relay cycling provides short, intense pulses of power to all the glow plugs simultaneously. This pulsed after glow sequencing, is maintained during the first few minutes of engine operation which helps reduce pollution and makes for a smoother initial operation. However, this after glow sequencing which activates all plugs simultaneously creates a large electromagnetic impulse, EMI, power surge each time the relay is cycled. Power surges of a magnitude in the 100 amp range for one second are common with the pulses being delivered every 5 to 10 seconds. The cycle time and frequency depend on the starting protocol programmed into the controller. The EMI surges create problems with radio systems on the vehicle and also the other electrically controlled systems on the vehicle.
Prior art systems are generally designed so the duty cycle is dependant on the temperature of a portion of the engine or cooling system at a location removed from the glow plugs. When the engine does not start promptly, the ignition is generally turned off and the starting sequence reinitiated. Since the temperature sensed by the controller has not generally changed markedly, the system will default to its cold start mode and the glow plugs will be reactivated for the full power preglow cycle of the starting protocol. Repeated use of the full power preglow cycle without an adequate cool down period, exposes the glow plugs to premature failure from overheating since the glow plugs are not designed to take the full power preglow energy cycle without a rest period. This type of failure is particularly a problem with many commercial and heavy equipment systems that are powered by 24 volt electrical systems. The higher voltage will over heat the glow plugs faster than 12 volt systems if the plugs preglow cycle is repeated without adequate rest time between cycles since most glow plugs are designed for 12 Volt systems. Failure modes from over heating range from the plugs simply burning out to the heating element breaking inside the engine head. A broken plug failure expands the glow plug element to the point where it can not be removed from the head using normal techniques and requires disassembly of the engine for repair.
It is desirable to create a starting assist system which will both ensure an adequate rest time between repeated pre-glow cycles and is not temperature dependant. Further the system should provide an after glow cycle protocol that maintains an even glow with minimum EMI spikes.